Systems and methods for equalizing backpressure in engine cylinders

ABSTRACT

An intake manifold is provided. A first inlet is structured to receive pressurized intake air from a turbocharger. A second inlet is structured to receive exhaust gas recirculation gas from an exhaust gas recirculation system. A third inlet is structured to receive fuel from a fuel line. A plurality of outlets are structured to be fluidly coupled to an engine. An intake manifold passage extends between each of the first, second, and third inlets, and the plurality of outlets. The intake manifold passage is shaped so as to cause at least two reversals in flow direction of each of the intake air, the exhaust gas recirculation gas, and the fuel through the intake manifold passage so as to improve mixing of each of the intake air, the exhaust gas recirculation gas, and the fuel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/889,058, filed on Jun. 1, 2020, which is a divisional of Ser. No.16/073,117, filed on Jul. 26, 2018, which is the U.S. National Phase ofPCT Application No. PCT/US2017/016027, filed on Feb. 1, 2017, whichclaims priority from U.S. Provisional Application No. 62/291,786, filedFeb. 5, 2016, the contents of which are incorporated herein by referencein their entireties.

TECHNICAL FIELD

The present disclosure relates generally to aftertreatment systems foruse with internal combustion (IC) engines.

BACKGROUND

Exhaust aftertreatment systems are used to receive and treat exhaust gasgenerated by engines such as IC engines. Conventional exhaust gasaftertreatment systems include any of several different componentsstructured to reduce the levels of harmful exhaust emissions present inexhaust gas. For example, certain exhaust aftertreatment systems fordiesel-powered IC engines include a selective catalytic reduction (SCR)system which includes a catalyst formulated to convert NO_(x) (NO andNO₂ in some fraction) into harmless nitrogen gas (N₂) and water vapor(H₂O) in the presence of ammonia (NH₃). A reductant is often insertedinto exhaust conduits communicating the exhaust gas to the SCR systemand/or other components of the aftertreatment system.

Natural gas as a fuel for heavy duty engines is receiving attention dueto its potential to reduce pollutant and greenhouse gas emissions.Generally, natural gas engines comprise diesel engines converted tooperate on natural gas, for example operating the diesel engine onnatural gas using spark ignition (SI) stoichiometric parameters. Forexample, some natural gas engines may comprise diesel engines spanning arange from 6.5 L to 12 L in displacement converted to operate as naturalgas engines. Such natural gas engines may be operated usingstoichiometric combustion with cooled exhaust gas recirculation andthree-way catalysis. However, simply converting diesel engines tooperate on natural gas may cause the engine to experience high thermalstresses; relatively low efficiency due to low volumetric efficiency andcompression ratio; unequal backpressure on engine cylinders, which maycause knock; and poor performance in terms of power and torque density,and transient response.

SUMMARY

Embodiments described herein relate generally to systems and methods forequalizing exhaust gas backpressure across a plurality of cylinders ofan engine and, in particular, to exhaust manifolds structured toequalize backpressure of an exhaust gas across the plurality ofcylinders of the engine.

In a first set of embodiments, an exhaust manifold comprises a pluralityof exhaust intake conduits. Each of the plurality of exhaust intakeconduits is structured to be fluidly coupled to an engine and structuredto receive exhaust gas from a corresponding cylinder of the engine. Atleast one of the plurality of exhaust intake conduits may provide areduction in an exhaust intake conduit cross-sectional area of therespective exhaust intake conduit from an exhaust intake conduit inletto an exhaust intake conduit outlet of the respective exhaust intakeconduits. The exhaust manifold also comprises a plurality of bends. Eachof the plurality of bends is defined by a respective one of the exhaustintake conduit outlets. The exhaust manifold also comprises an exhaustintake manifold fluidly coupled to the exhaust intake conduit outlet ofat least a portion of the plurality of exhaust intake conduits. Each ofthe plurality of bends is shaped so as to define an angle of approach ofexhaust gas flowing through the respective exhaust intake conduitoutlet. A first angle of approach of the first bend relative to theexhaust intake manifold flow axis is smaller than a second angle ofapproach of a second bend of the plurality of bends. The first bend isstructured to receive exhaust gas from a first cylinder of the engineand the second bend is structured to receive exhaust gas from a secondcylinder of the engine. The first cylinder is positioned in an outerposition on the engine relative to the second cylinder.

In another set of embodiments, a system comprises an engine comprising aplurality of cylinders. Each of the plurality of cylinders is structuredto burn a fuel so as to produce an exhaust gas. The system also includesan exhaust manifold comprising a plurality of exhaust intake conduits.Each of the plurality of exhaust intake conduits is structured to befluidly coupled to an engine and structured to receive exhaust gas froma corresponding cylinder of the engine. The exhaust manifold alsoincludes at least one exhaust intake manifold. The exhaust intakeconduit outlet of at least a portion of the plurality of exhaust intakeconduits is fluidly coupled to the at least one exhaust intake manifold.The exhaust manifold also includes a means for equalizing a pressurepulse amplitude caused by combustion in each of the plurality ofcylinders.

In another set of embodiments, an exhaust manifold includes a firstexhaust intake conduit structured to be fluidly coupled to an engine andstructured to receive exhaust gas from a first cylinder of the engine. Asecond exhaust intake conduit is structured to be fluidly coupled to anengine and structured to receive exhaust gas from a second cylinder ofthe engine. The engine has a plurality of cylinders with the firstcylinder being positioned in an outer position on the engine relative tothe second cylinder. The first bend defines an oval-shapedcross-section. The first bend is shaped so as to define a first angle ofapproach of exhaust gas flowing through the first exhaust intake conduitoutlet. A second bend is defined by a second exhaust intake conduitoutlets of the second exhaust intake conduit. The second bend is shapedso as to define a second angle of approach of exhaust gas flowingthrough the second exhaust intake conduit outlet. An exhaust intakemanifold is fluidly coupled to each of the first and second exhaustintake conduits. The exhaust intake manifold defines a firstcross-sectional area proximate the first exhaust intake conduit and asecond cross-sectional area proximate the second exhaust intake conduit.The first cross-sectional area is larger than the second cross-sectionalarea. The exhaust intake manifold defines an exhaust intake manifoldflow axis. The first angle of approach relative to the exhaust intakemanifold flow axis is smaller than the second angle of approach.

In another set of embodiments, an exhaust manifold includes a pluralityof exhaust intake conduits. Each of the plurality of exhaust intakeconduits is structured to be fluidly coupled to an engine and structuredto receive exhaust gas from a corresponding cylinder of the engine. Anexhaust intake manifold is fluidly coupled to an exhaust intake conduitoutlet of at least one of the plurality of exhaust intake conduits. Eachof the plurality of exhaust intake conduits and the exhaust intakemanifold define an exhaust intake manifold core volume. Each of theplurality of exhaust intake conduits and the exhaust intake manifold areshaped so as to define the exhaust intake manifold core volume based oneach of the displacement of the engine, the intended operating power ofthe engine, and the intended flow rate of the exhaust gas through theexhaust manifold.

In another set of embodiments, an intake manifold includes a first inletstructured to be fluidly coupled to a turbocharger so as to receivepressurized intake air from the turbocharger. A second inlet isstructured to be fluidly coupled to an exhaust gas recirculation (EGR)system so as to receive EGR gas from the EGR system. A third inlet isstructured to be fluidly coupled to a fuel line so as to receive fuelfrom the fuel line. A plurality of outlets are structured to be fluidlycoupled to an engine. An intake manifold passage extends between each ofthe first, second, and third inlets, and the plurality of outlets. Theintake manifold passage is shaped so as to cause at least two reversalsin flow direction of each of the intake air, the EGR gas, and the fuelthrough the intake manifold passage so as to improve mixing of each ofthe intake air, the EGR gas, and the fuel.

It should be appreciated that all combinations of the foregoing conceptsand additional concepts discussed in greater detail below (provided suchconcepts are not mutually inconsistent) are contemplated as being partof the subject matter disclosed herein. In particular, all combinationsof claimed subject matter appearing at the end of this disclosure arecontemplated as being part of the subject matter disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several implementations in accordance withthe disclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings.

FIG. 1 is a schematic illustration of system including an exhaustmanifold, according to an embodiment.

FIG. 2A is a side view and FIG. 2B is a bottom view of at least aportion of the exhaust manifold of FIG. 1 .

FIG. 2C is a side view of a portion of the exhaust manifold of FIGS. 2Aand 2B.

FIG. 3 is a schematic flow diagram of various operational parameters ofa natural gas engine converted from a diesel engine which were alteredto obtain high efficiency of the natural gas engine.

FIG. 4 is a top view of a system that includes an engine, an intakemanifold and an exhaust manifold, according to an embodiment.

FIG. 5A is a top view and FIG. 5B is a front view of the intake manifoldand the exhaust manifold included in the system of FIG. 4 .

FIG. 5C is a schematic diagram of the exhaust manifold included in thesystem of FIG. 4 .

FIG. 6A is a perspective view of the exhaust manifold of the system ofFIG. 3 fluidly coupled to a turbine and FIG. 6B shows the exhaustmanifold and turbine with covers assembled thereon.

FIG. 7 is a perspective view of an EGR assembly included in the systemof FIG. 3 .

FIG. 8A-B are finite element analysis (FEA) models illustrating heattransfer coefficients in water jackets around valve seats, bridges andan ignitor core of a cylinder included in the engine of FIG. 3 (FIG. 8A)and predicted combustion face temperature and location of maxtemperature (FIG. 8B).

FIG. 9 is a schematic illustration of a compressor recirculation system.

FIG. 10 is a plot of impact of EGR on gross indicated efficiency of theengine.

FIG. 11A is a plot of burn duration and FIG. 11B is a plot of ignitiondelay vs. crank angle of 50% (CA50) variations.

FIG. 12 is a plot of indicated fuel consumption of the engine.

FIG. 13 is a plot of premix air/fuel mixture injection and port fuelinjection (PFI) in each cylinder of the engine of FIG. 3 .

FIG. 14 is a plot of apparent heat release vs. crank angle of a crankshaft of the engine of FIG. 3 operated using PFI.

FIG. 15 is a computational fluid dynamic (CFD) model showing modeledperformance of the intake system included in the system of FIG. 3 .

FIG. 16 are bar charts summarizing turbine loss factors.

FIG. 17 is a schematic illustration of an air handling architecture.

FIG. 18A is a plot of fresh air flow and FIG. 18B is a plot of EFRFraction tracking during a federal testing procedure (FTP) cycle.

FIG. 19 is a schematic illustration of an air/fuel ratio control system.

FIGS. 20A-B are plots of air estimator performance at speed A (FIG. 20A)and speed B (FIG. 20B).

FIGS. 21A-D are plots demonstrating the influence of outer loop onconstituents of an exhaust gas emitted from the system of FIG. 3 .

FIGS. 22A-C are plots of NO_(x), (FIG. 22A), methane (FIG. 22B) and CO(FIG. 22C) emissions during heavy-duty cold FTP transient cycle. Theemissions were report at engine out (EO), close-coupled catalyst out(CC) and system out (SO) locations.

FIGS. 23A-C are plots of NOR, (FIG. 23A), methane (FIG. 23B) and CO(FIG. 23C) emissions during heavy-duty warm FTP transient cycle. Theemissions were reported at engine out (EO), close-coupled catalyst out(CC) and system out (SO) locations.

FIG. 24A is a plot of cumulative NO_(x) and FIG. 24B is a plot ofcumulative methane (CH₄) cold FTP transient cycle conversion performancepredictions against testing data.

FIG. 25 includes plots of a peak cylinder pressure (PCP) and CA50variations of a baseline and a new engine.

FIGS. 26A-B are FEA models comparing a combustion face temperature ofthe baseline engine (FIG. 26A) and a new engine (FIG. 26B).

FIG. 27 is a plot of EGR fraction vs. engine pressure change or deltapressure (DP).

FIG. 28 is a plot of knock vs. EGR fraction.

FIG. 29 is a plot of air flow and EGR fraction vs time.

FIG. 30 is a plot of emission results for cold/hot FTP emissions test.

FIG. 31 is a plot of cycle brake thermal efficiency (BTE) vs. lowerheating value.

Reference is made to the accompanying drawings throughout the followingdetailed description. In the drawings, similar symbols typicallyidentify similar components, unless context dictates otherwise. Theillustrative implementations described in the detailed description,drawings, and claims are not meant to be limiting. Other implementationsmay be utilized, and other changes may be made, without departing fromthe spirit or scope of the subject matter presented here. It will bereadily understood that the aspects of the present disclosure, asgenerally described herein, and illustrated in the figures, can bearranged, substituted, combined, and designed in a wide variety ofdifferent configurations, all of which are explicitly contemplated andmade part of this disclosure.

DETAILED DESCRIPTION

Embodiments described herein relate generally to systems and methods forequalizing exhaust gas backpressure across a plurality of cylinders ofan engine and, in particular, to exhaust manifolds structured toequalize backpressure of an exhaust gas across the plurality ofcylinders of the engine.

Natural gas as a fuel for heavy duty engines is receiving attention dueto its potential to reduce pollutant and greenhouse gas emissions.Generally, natural gas engines comprise diesel engines converted tooperate on natural gas, for example operating the diesel engine onnatural gas using SI stoichiometric parameters. For example, somenatural gas engines may comprise diesel engines spanning a range from6.5 L to 12 L in displacement converted to operate as natural gasengines. Such natural gas engines may be operated using stoichiometriccombustion with cooled exhaust gas recirculation and 3-way catalysis.

However, simply converting diesel engines to operate on natural gas maycause the engine to experience high thermal stresses; relatively lowefficiency due to low volumetric efficiency and compression ratio;unequal backpressure on engine cylinders which may cause knock; and poorperformance in terms of power and torque density, and transientresponse. For example, the backpressure exerted by the exhaust gasflowing out of individual cylinders of engines (e.g., natural gasengines converted from diesel engines) may vary across the plurality ofcylinders. This may lead to inconsistent temperatures across theplurality of cylinders, which may cause at least a portion of theplurality of cylinders included in the engine to run “hot” (e.g., at atemperature exceeding a design temperature of the respective cylinder).This can cause engine “knock” or pre-ignition, which further reduces theefficiency of the engine.

Various embodiments of the systems and methods described herein mayprovide benefits over conventional engine systems, including, forexample: (1) equalizing pressures across cylinders, such as via anexhaust manifold structured to equalize a backpressure exerted by theexhaust gas on each of a plurality of cylinders of an engine; (2)maintaining a consistent temperature across all of the plurality ofcylinders of the engine so as to reduce knock, thereby increasing engineefficiency; (3) providing continuous area reduction of exhaust gas flowto a turbine fluidly coupled to the engine so as to maintain exhaust gasmomentum and reduce flow losses; (4) aligning a trajectory of theexhaust gas flow into an EGR system so as to maximize momentum recoveryinto the EGR flow path; and (5) defining cross-sections structured tomaintain attachment of the exhaust gas flow to walls of the exhaustmanifold or components thereof, thereby reducing turbulence and/ormomentum losses.

FIG. 1 is a schematic illustration of a system 100, according to anembodiment. The system 100 comprises an engine 102, an exhaust manifold110, and optionally a turbine 160 and an EGR assembly 170.

The engine 102 comprises an engine block 104 within which a plurality ofcylinders 106 are defined. Each of the plurality of cylinders 106 isstructured to burn fuel (e.g., natural gas) so as to produce an exhaustgas. The engine 102 may include a diesel engine, a natural gas engine, agasoline engine, a biodiesel engine, an LPG engine, a dual-fuel engine,or any other suitable engine. In particular embodiments, the engine 102may include a diesel engine converted to operate on natural gas. Inother embodiments, the engine 102 is specifically designed to operate onnatural gas.

The exhaust manifold 110 is fluidly coupled to the engine 102 andstructured to receive the exhaust gas from the engine 102. The exhaustmanifold 110 is structured to equalize a pressure pulse amplitude causedby combustion in each of the plurality of cylinders 106 of the engine102. This is also referred to herein as equalizing a backpressureexerted by the exhaust gas on each of the plurality of cylinders 10. Asused herein, the term “equalize” refers to achieving less than 10%variation in pressure pulse amplitudes in the exhaust manifold 110caused by combustion in each of the plurality of cylinders 106. Inparticular implementations, the exhaust manifold 110 is structured suchthat equalizing pressure pulse amplitude achieves less than 5% variationbetween cylinders 106. In further implementations, the exhaust manifold110 is structured such that equalizing pressure pulse amplitude achievesless than 3% variation between cylinders 106. In some embodiments, theexhaust manifold 110 may also cause a temperature of each of theplurality of cylinders 106 to be substantially the same (e.g., within+/−5% to +/−10% of each other, inclusive of all ranges and valuestherebetween). The consistent pressure and temperature across theplurality of cylinders 106 may reduce knock, thereby minimizing lossesin the efficiency of the engine 102.

Expanding further, the exhaust manifold 110 may comprise a plurality ofexhaust intake conduits 112. Each of the plurality of exhaust intakeconduits 112 is structured to be fluidly coupled to the engine 102 andstructured to receive exhaust gas from a corresponding cylinder 106 ofthe engine 102. Each of the plurality of exhaust intake conduits 112 mayprovide a reduction in an exhaust intake conduit cross-sectional area ofthe exhaust intake conduit 112 from an exhaust intake conduit inlet toan exhaust intake conduit outlet thereof. The exhaust manifold 110 alsocomprises at least one exhaust intake manifold 114. The exhaust intakeconduit outlet of at least a portion of the plurality of exhaust intakeconduits 112 is fluidly coupled to the at least one exhaust intakemanifold 114.

For example, as shown in FIG. 1 and FIGS. 2A-C, the exhaust manifold 110may comprise a first exhaust intake manifold 114 a and a second exhaustintake manifold 114 b (collectively referred to as “the exhaust intakemanifolds 114”). The exhaust manifold 110 may also comprise a first setof exhaust intake conduits 112 a and a second set of exhaust intakeconduits 112 b (collectively referred to herein as the “exhaust intakeconduits 112”). The first set of exhaust intake conduits 112 a isfluidly coupled to the first exhaust intake manifold 114 a andstructured to receive exhaust gas from a first portion of the pluralityof cylinders 106. Furthermore, the second set of exhaust intake conduits112 b are fluidly coupled to the second exhaust intake manifold 114 band structured to receive exhaust gas from a second portion of theplurality of cylinders 106.

A cross-section of the exhaust intake conduit inlet may be larger than across-section of the exhaust intake conduit outlet, thereby causing theexhaust intake conduit cross-sectional area of each of the exhaustintake conduits 112 to decrease from the exhaust intake conduit inlet tothe exhaust intake conduit outlet thereof. This may accelerate theexhaust gas flow towards the exhaust intake manifolds 114, therebypreventing any loss in momentum or pressure of the exhaust gas as itflows into the exhaust intake conduits 112.

In some embodiments, the exhaust intake conduit outlet of each of theplurality of exhaust intake conduits 112 comprises a bend 113 where itis coupled to the corresponding exhaust intake manifold 114. Moreover,in some embodiments, the exhaust intake conduit outlet of at least onethe plurality of exhaust intake conduits 112 defines a non-circularcross-section (e.g., an elliptical or oval-shaped cross-section), forexample at the bend 113. The non-circular cross-section may prevent theexhaust gas from separating from inner surfaces of sidewalls of theexhaust intake conduits 112 as the exhaust gas enters the exhaust intakemanifolds 114, thereby preventing flow losses.

The reduction in the cross-sectional area of the exhaust intake conduits112 and/or the bends 113 provided therein may serve to equalize abackpressure exerted by the exhaust gas on each of the plurality ofcylinders 106. This may also cause a temperature in each of theplurality of the cylinders 106 to be substantially the same, therebyreducing knock.

In some embodiments, the exhaust intake manifolds 114 may also define across-sectional area that reduces from a portion where the exhaust gasenters the exhaust intake manifolds 114 to a portion where the exhaustgas exits the exhaust intake manifold 114. The reducing cross-sectionalarea of the exhaust intake manifold 114 may further facilitateequalizing of a backpressure exerted by the exhaust gas on each of theplurality of cylinders 106, for example by preventing momentum losses ofthe exhaust gas.

A first outlet port 116 a and a second outlet port 116 b (collectivelyreferred to herein as “the outlet ports 116”) may be fluidly coupled tothe first exhaust intake manifold 114 a and the second exhaust intakemanifold 114 b. Each of the outlet ports 116 defines an outlet port flowaxis 117, which is positioned orthogonal (e.g., at an angle in the rangeof 60 degrees to 120 degrees inclusive of all ranges and valuestherebetween) to an exhaust intake manifold flow axis 120 of the exhaustintake manifolds 114. In some embodiments, the outlet port flow axis 117may be parallel to and/or in line with an exhaust intake conduit flowaxis 123 of the plurality of exhaust intake conduits 112 so as tominimize the number of turns the exhaust gas experiences from theexhaust intake conduits 112 to the turbine 160.

The outlet ports 116 may provide a reduction in an outlet portcross-sectional area of the outlet ports 116 from an outlet port inletto an outlet port outlet of each of the outlet ports 116. Furthermore,each of the outlet ports 116 may define a non-circular (e.g., anelliptical or oval-shaped) cross-section. The reduction incross-sectional area and/or the elliptical or oval cross-section of theoutlet ports 116 may also serve to equalize the backpressure exerted bythe exhaust gas on each of the plurality of cylinders 106.

The outlet ports 116 may be fluidly coupled to the turbine 160 (e.g., aturbine included in a turbocharger). The reducing cross-sectional areaand/or the elliptical or oval cross-section of the outlet ports 116 mayprovide uniform flow of the exhaust gas into the turbine 160. The firstoutlet port 116 a and the second outlet port 116 b may provide a fullydivided flow of the exhaust gas received from the respective first setand the second set of the plurality of cylinders 106 to the turbine 160,which may also serve to equalize the backpressure of the exhaust gas oneach of the plurality of cylinder 106.

In some embodiments, at least one pull-off conduit may be fluidlycoupled to the at least one exhaust intake manifold 114. At least aportion of the at least one pull-off conduit may define a pull-offconduit flow axis 126 positioned orthogonal to each of the exhaustintake manifold flow axis 120 and the outlet port flow axis 117. Invarious embodiments, a pull-off conduit first portion of the at leastone pull-off conduit may define a reducing pull-off conduitcross-sectional area from a pull-off conduit first portion inlet to apull-off conduit first portion outlet of the pull-off conduit firstportion.

For example, as shown in FIG. 1 , the exhaust manifold 110 may include afirst pull-off conduit 118 a and a second pull-off conduit 118 b(collectively referred to herein as “the pull-off conduits 118”) fluidlycoupled to the first exhaust intake manifold 114 a and the secondexhaust intake manifold 114 b, respectively.

At least a portion of the pull-off conduits 118 which is fluidly coupledto the exhaust intake manifolds 114 may be positioned orthogonal (e.g.,at an angle in the range of 60 degrees to 120 degrees, inclusive of allranges and values therebetween) to each of the exhaust intake manifoldflow axis 120 of the exhaust intake manifolds 114 and the outlet portflow axis 117 of the outlet ports 116. For example, the pull-offconduits 118 may be positioned orthogonal to the exhaust intakemanifolds 114 in a first plane (e.g., in an X-Y plane) and orthogonal tothe outlet ports 116 in a second plane (e.g., in a Y-Z plane).

A pull-off conduit first portion 119 a/b of the pull-off conduits 118a/b may define a reducing pull-off conduit cross-sectional area from apull-off conduit first portion inlet to a pull-off conduit first portionoutlet of the pull-off conduit first portion 119 a/b. The reducingcross-sectional area may serve to maintain the momentum of the exhaustgas flowing through the pull-off conduit first portion 119 a/b, therebyreducing flow losses.

The pull-off conduit first portion 119 a/b of the pull-off conduits 118a/b are fluidly coupled to each other at a joint 121 so as to define asingle flow path for the exhaust gas downstream of the joint 121. Thesingle flow path reduces in cross-sectional area until it reaches apull-off conduit first portion outlet 122 or throat. The sidewalls ofthe first portion 119 a/b of the pull-off conduits 118 a/b are joinedwith each other at the joint 121 at a sufficiently small angle (e.g.,less than 5 degrees) so that the portions of the exhaust gas flowinginto the joint 121 towards the pull-off conduit first portion outlet 122from each of the pull-off conduit first portions 119 a/b may experienceminimal turbulence and smoothly mix with each other. A cross-sectionalarea of the pull-off conduit first portion outlet 122 may be optimizedso as to prevent the exhaust gas from experience sudden momentum of flowlosses, which may change the backpressure exerted by the exhaust gas onone or more of the plurality of cylinders 106.

The exhaust manifold 110 may also include a diffuser 128. The diffuser128 may have a larger cross-sectional area relative to a cross-sectionalarea of the pull-off conduits 118 so as to reduce a velocity of theexhaust gas flowing therethrough, expand the exhaust gas, and/or reducea temperature thereof. The diffuser 128 may be coupled to an EGRassembly 170, which may be structured to communicate the portion of theexhaust gas entering the pull-off conduits 118 to the plurality ofcylinders 106, for example, to cool the combustion temperature of theair/fuel mixture therein (e.g., to reduce knock).

The pull-off conduits 118 may include a pull-off conduit second portion124 fluidly coupled to each of the diffuser 128 and the pull-off conduitfirst portion outlet 122. The pull-off conduit second portion 124 maydefine an expanding cross-sectional area from the pull-off conduit firstportion outlet 122 to a pull-off conduit second portion outlet of thepull-off conduit second portion 124. The pull-off conduit second portionoutlet is fluidly coupled to the diffuser 128.

The expanding cross-sectional area of the pull-off conduit secondportion 124 may provide smooth reduction in pressure and flow velocityof the exhaust gas from the pull-off conduits 118 to the diffuser 128.This may prevent vortices, flow losses, or sudden variations inbackpressure of the exhaust gas. The pull-off conduit second portion 124may also include a first bend 125 and a second bend 127 leading to thediffuser 128. The first bend 125 and the second bend 127 may define anelliptical or oval cross-section which may cause the exhaust gas flow toremain attached to an inner surface of the sidewalls of the pull-offconduit second portion 124, thereby preventing flow losses.

In some embodiments, an upstream portion of the pull-off conduit secondportion 124 may define a smaller change in cross-sectional area from aninlet to an outlet thereof, relative to a downstream portion of thepull-off conduit second portion 124. The smaller change incross-sectional area of the upstream portion relative to the downstreamportion may provide a controlled reduction in exhaust gas momentum andvelocity leading to the diffuser 128 so as to prevent sudden changes inbackpressure of the exhaust gas.

FIG. 2A is a side view of at least a portion of the engine 102 and theexhaust manifold 110 of FIG. 1 . FIG. 2B is a bottom view of at least aportion of the exhaust manifold 110 of FIG. 1 . As illustrated in FIG.2A, the cylinders 106 of the engine 102 include a first cylinder 130, asecond cylinder 132, a third cylinder 134, a fourth cylinder 136, afifth cylinder 138, and a sixth cylinder 140. All of the cylinders 106are arranged in the engine 102 in a line, with the first and sixthcylinders 130, 140 being positioned in an outer-most position on theengine 102, the third and fourth cylinders 134, 136 being positioned inan inner-most position on the engine 102, and the second and fifthcylinders 132, 138 being positioned in an intermediate position on theengine 102 between the outer-most and inner-most cylinders 106. As usedherein, the terms “outer” and “inner,” in regard to the position of thecylinders 106 on the engine 102, refers to the position of each of thecylinders 106 on the engine relative to the other cylinders 106. Anouter-most cylinder 106 (e.g., the first cylinder 130) is positionedadjacent one other cylinder (e.g., the second cylinder 132). Innercylinders (e.g., the second cylinder 132) are positioned adjacent twoother cylinders (e.g., the first and third cylinders 130, 134).

Similarly, the exhaust intake conduits 112 of the exhaust intakemanifolds 114 include a first exhaust intake conduit 142, a secondexhaust intake conduit 144, a third exhaust intake conduit 146, a fourthexhaust intake conduit 148, a fifth exhaust intake conduit 150, and asixth exhaust intake conduit 152. The first exhaust intake conduit 142is structured to be fluidly coupled to the first cylinder 130; thesecond exhaust intake conduit 144 is structured to be fluidly coupled tothe second cylinder 132; the third exhaust intake conduit 146 isstructured to be fluidly coupled to the third cylinder 134; the fourthexhaust intake conduit 148 is structured to be fluidly coupled to thefourth cylinder 136; the fifth exhaust intake conduit 150 is structuredto be fluidly coupled to the fifth cylinder 138; and the sixth exhaustintake conduit 152 is structured to be fluidly coupled to the sixthcylinder 140. Accordingly, the first and sixth exhaust intake conduits142, 152 are positioned in an outer-most position on the engine 102; thethird and fourth exhaust intake conduits 144, 148 are positioned in aninner-most position on the engine 102; and the second and fifth exhaustintake conduits 146, 150 are positioned in an intermediate position onthe engine 102 between the outer-most and inner-most exhaust intakeconduits 112. As mentioned above, at least one of the exhaust intakemanifolds 114 define a cross-sectional area that reduces from a portionwhere the exhaust gas enters the respective exhaust intake manifolds 114to a portion where the exhaust gas exits the respective exhaust intakemanifolds 114. Additionally, in some embodiments, the exhaust intakemanifolds 114 define cross-sectional areas that are different based onthe intended position of the exhaust intake manifolds 114 on the engine102. For example, in some embodiments, the exhaust intake manifolds 114define a cross-sectional area that reduces from an outer-most positionto an inner-most position, as defined based on the intendedconfiguration of the exhaust intake manifolds 114 when installed on theengine 102. This is most clearly shown in FIG. 2B. In other words, theexhaust intake manifolds 114 define a larger cross-sectional areaproximate an outer cylinder 106 than proximate an inner cylinder 106.For example, in some embodiments, the first exhaust intake manifold 114a defines a first cross-sectional area proximate the first exhaustintake conduit 142 and a second cross-sectional area proximate the thirdexhaust intake conduit 146, the second cross-sectional area beingsmaller than the first cross-sectional area.

FIG. 2C is a side view of a portion of the exhaust manifold 110 of FIGS.2A and 2B. As mentioned above, the exhaust manifold 110 includes severaldesign features that are implemented to achieve various designobjectives, such as equalizing a backpressure exerted by the exhaust gason each of a plurality of cylinders of the engine 102 or equalizing apressure pulse amplitude at a point in the exhaust manifold 110 (e.g.,proximate the outlet ports 116) caused by combustion in each of theplurality of cylinders of the engine 102. Another design objective is tomaximize the total pressure of the exhaust gas so as to optimizeoperation of the turbine 160 and the EGR assembly 170. For example, insome embodiments, the shape of various portions of each of the exhaustintake conduits 112 and the exhaust intake manifolds 114 is defined sothat exhaust gas flowing through the respective exhaust intake conduits112 and exhaust intake manifolds 114 causes the same pressure pulseamplitude at a point in the exhaust manifold 110. In other words, theexhaust gas “acts the same” regardless of the cylinder from which it wasexpelled. Additionally, the shape of various portions of each of theexhaust intake conduits 112 and the exhaust intake manifolds 114 isdefined so as to maximize the pressure of the exhaust gas flowingthrough the respective exhaust intake conduits 112 and exhaust intakemanifolds 114.

As will be explained in further detail below, in some embodiments, atleast three design parameters are defined so as to equalize the pressurepulse amplitude in the exhaust manifold 110. First, at least one of thebends of the respective exhaust intake conduit outlets has anon-circular (e.g., oval or elliptical) cross-section. Second, at leastone of the exhaust intake conduits defines a cross-sectional area thatreduces from the exhaust intake conduit inlet to the exhaust intakeconduit outlet. Third, each of the plurality of bends are shaped so asto define particular angles of approach of exhaust gas flowing throughthe respective exhaust intake conduit outlet. As will be appreciated,each of these design parameters was defined so as to achieve the designobjectives.

As illustrated in FIG. 2C, each of the exhaust intake conduits 112includes an exhaust intake conduit inlet and an exhaust intake conduitoutlet. In operation, exhaust gas flows from the exhaust intake conduitinlet, through the exhaust intake conduit 112, out of the exhaust intakeconduit outlet, and into the exhaust intake manifold 114. For example,as illustrated in FIG. 2A, the first exhaust intake conduit 142 includesa first exhaust intake conduit inlet 172 and a first exhaust intakeconduit outlet 174; the second exhaust intake conduit 144 includes asecond exhaust intake conduit inlet 176 and a second exhaust intakeconduit outlet 178; and the third exhaust intake conduit 146 includes athird exhaust intake conduit inlet 179 and a third exhaust intakeconduit outlet 182.

As also mentioned above, each of the exhaust intake conduit outlets 174,178, 182 define a bend where the respective exhaust intake conduitoutlets 174, 178, 182 is coupled to the exhaust intake manifold 114. Forexample, as illustrated in FIG. 2C, the first exhaust intake conduitoutlet 174 defines the first bend 113, the second exhaust intake conduitoutlet 178 defines a second bend 184, and the third exhaust intakeconduit outlet 182 defines a third bend 186.

In some embodiments, at least one of the first, second, and third bends113, 184, 186 defines a non-circular (e.g., oval or elliptical)cross-section. For example, in some embodiments, the first bend 113defines a non-circular cross-section. In some embodiments, the secondand third bends 184, 186 do not define a non-circular cross-section. Inother embodiments, each of the first, second, and third bends 113, 184,186 defines a non-circular cross-section.

In some embodiments, at least one of the exhaust intake conduits 112defines a cross-sectional area that reduces from the exhaust intakeconduit inlet to the exhaust intake conduit outlet. For example, in oneembodiment, the third exhaust intake conduit 146 defines across-sectional area that reduces from the third exhaust intake conduitinlet 180 to the third exhaust intake conduit outlet 182. In someembodiments, the first exhaust intake conduit 142 defines across-sectional area that does not reduce from the first exhaust intakeconduit inlet 172 to the first exhaust intake conduit outlet 174. Insome embodiments, the exhaust intake conduits 112 that are configured tobe positioned proximate inner cylinders on the engine 100 define across-sectional area that reduces from the exhaust intake conduit inletto the exhaust intake conduit outlet to a greater extent than thoseexhaust intake conduits 112 positioned on outer cylinders of the engine100.

In some embodiments, each of the exhaust intake conduits 112 include across-sectional area that defines an area schedule between the exhaustintake conduit inlet and the exhaust intake conduit outlet. For example,the first exhaust intake conduit 142 includes a first cross-sectionalarea that varies along its length, thereby defining a first areaschedule between the first exhaust intake conduit inlet 172 and thefirst exhaust intake conduit outlet 174; the second exhaust intakeconduit 144 includes a second cross-sectional area that defines a secondarea schedule between the second exhaust intake conduit inlet 176 andthe second exhaust intake conduit outlet 178; and the third exhaustintake conduit 146 includes a third cross-sectional area that defines athird area schedule between the third exhaust intake conduit inlet 179and the third exhaust intake conduit outlet 182. In some embodiments,the area schedules are defined by both the exhaust intake conduits 112and the exhaust intake manifold 114. For example, in some embodiments,the first area schedule is defined by the cross-sectional diameter ofthe first exhaust intake conduit 142 from the first exhaust intakeconduit inlet 172 to the first exhaust intake conduit outlet 174, andfurther to the first exhaust intake manifold 114 a to a point proximate(e.g., upstream of) the first outlet port 116 a.

In some embodiments, the first area schedule is linear. In other words,the cross-sectional area of the first exhaust intake conduit 142decreases at a linear rate from a first cross-sectional diameter at thefirst exhaust intake conduit inlet 172 to a smaller second diameter atthe first exhaust intake conduit outlet 174. In some embodiments, thesecond and third area schedules are non-linear. In other words, forexample, the cross-sectional area of the second exhaust intake conduit144 decreases from a first cross-sectional diameter at the secondexhaust intake conduit inlet 176 to a smaller second diameter at thesecond exhaust intake conduit outlet 178 at a non-linear rate. Thenon-linear area schedule is most clearly shown by the third exhaustintake conduit 146. As shown in FIG. 2C, the “necking” at the thirdexhaust intake conduit outlet 182 causes the third area schedule to benon-linear due to the sharp reduction in cross-sectional diameterproximate the third bend 186.

The area schedules also define an exhaust intake manifold core volume.For example, in one embodiment, a first exhaust intake manifold corevolume is the internal volume of the structure that defines theplurality of exhaust intake conduits 112 a and the first exhaust intakemanifold 114 a of the exhaust manifold 110. In one embodiment, the firstexhaust intake manifold core volume is the volume of the plurality ofexhaust intake conduits 112 a and the first exhaust intake manifold 114a upstream of the first outlet port 116 a. In some embodiments, theexhaust manifold 110 is sized so as to define the exhaust intakemanifold core volume relative to the displacement of the engine 100,based on a volume ratio. In other embodiments, the exhaust manifold 110is sized based on other factors, such as intended operating power of theengine 100 or intended flow rate of exhaust gas through the exhaustmanifold 110. For example, in some embodiments, the exhaust manifold 110is sized larger for larger engine displacement, higher intendedoperating power, and/or higher intended exhaust gas flow rate.

Each of the first, second, and third bends 113, 184, 186 are also shapedso as to define an angle of approach of exhaust gas flowing through therespective exhaust intake conduit outlet 174, 178, 182. The angles ofapproach may be defined, for example, relative to the exhaust intakemanifold flow axis 120. For example, the first bend 113 is shaped so asto define a first angle of approach 188; the second bend 184 is shapedso as to define a second angle of approach 190; and the third bend 186is shaped so as to define a third angle of approach 192. The angles ofapproach 188, 190, 192 are defined so as to minimize recirculationcaused by the exhaust gas impacting the walls of the exhaust intakemanifold 114. In some embodiments, the first angle of approach 188 issmaller than each of the second and third angles of approach 190, 192.In other words, in some embodiments, the angle of approach is smallerfor exhaust intake conduits 112 structured to be positioned in outerpositions on the engine 100. While FIGS. 1 and 2A-2B show an exhaustmanifold structured to reduce exhaust gas backpressure which may lead toreduced knock and increase in efficiency of the engine (e.g., a dieselengine converted into a natural gas engine) various other parameters andstructures of the engine may also be structured to improve an efficiencyof the engine. For example, FIG. 3 shows a family tree of variousparameters of an engine that may be structured to increase an efficiencyof an engine, for example a diesel engine converted into a natural gasengine.

FIG. 4 is a top perspective view of a system 200, according to anotherembodiment. The system 200 includes an engine 202, an exhaust manifold210, an intake manifold 250 and a turbine 260. In some embodiments, theengine 202 may include a 15 liter engine having six in-line cylindershaving a bore of 137 mm and stroke of 169 mm, a power of up to 447 kW,and torque of up to 2.779 Nm at 1,200 rpm.

The exhaust manifold is fluidly coupled to the engine 202. The exhaustmanifold 210 may be substantially similar to the exhaust manifold 110(FIG. 1 ) and, therefore, not described in further detail herein.Various portions of the system 200 and their novel features which leadto an increase in efficiency of the engine 202 are described below.

Intake Manifold and Port Breathing

One objective of increasing engine 202 efficiency is to reducevariations in operational parameters from cylinder-to-cylinder and fromcycle-to-cycle. The major contributors impacting efficiency of theengine 202 include the intake manifold 250, the exhaust manifold 210 andports for more efficient air handling. The intake manifold 250 and theports are structured so as to increase the efficiency of the engine 202.For example, the intake manifold 250 is structured so as to receive eachof pressurized intake air from the turbocharger, EGR gas, and fuelinjection. As shown in FIG. 4 , the intake manifold 250 is “S-shaped”such that the intake charge air including EGR gas and fuel is subjectedto at least two flow reversals before entering the engine 202, whichimproves constituent mixing of the intake charge air, the EGR gas, andthe fuel.

In one embodiment, the intake manifold 250 includes a first inlet 251, asecond inlet 253, and a third inlet 255. The first inlet 251 isstructured to be fluidly coupled to a turbocharger 257 so as to receivepressurized intake air from the turbocharger 257. The second inlet 253is structured to be fluidly coupled to an EGR system 258 so as toreceive EGR gas from the EGR system 258. The third inlet 255 isstructured to be fluidly coupled to a fuel line 259 so as to receivefuel from the fuel line 259. The intake manifold 250 also includes aplurality of outlets structured to be fluidly coupled to the engine 202.The intake manifold 250 further includes an intake manifold passageextending between each of the first, second, and third inlets, 251, 253,255 and the plurality of outlets. The intake manifold passage is shapedso as to cause at least two reversals in flow direction of each of theintake air, the EGR gas, and the fuel through the intake manifoldpassage so as to improve mixing of each of the intake air, the EGR gas,and the fuel.

The intake ports may have a patterned design, and are exactly the sameand all exhaust ports are exactly the same. The intake manifold 250includes individual, drop-down runners from the plenum thereof to theintake ports thereof. All cylinders of the engine 202 pull off chargeflow in exactly the same manner and there is no crosstalk betweencylinders.

The intake manifold 250 provides a long mixing length so as to achieveflow uniformity. The intake ports of the intake manifold 250 aresufficiently large so as to reduce flow losses into the cylinder.Furthermore, exhaust ports of the exhaust manifold 210 are smaller forhigher velocity flow to support the pulse EGR system 270 (see FIG. 7 ).The exhaust manifold 210 provides a fully divided, pulse capture flow tothe EGR 270 and isolates the front bank from the rear bank. Moreover,the trajectory and area schedule of exhaust and EGR system components isoptimized to reduce backpressure of the exhaust gas.

The cylinder head of the engine 202 comprises a Big Intake Small Exhaust(BISE) diamond valve pattern. The diamond pattern allows for generationof swirl and the bigger intake valves enable bigger intake ports,contributing to improved engine breathing. The intake ports have highflow capability and low losses. The intake manifold may comprise a frontend-inlet design with the plenum above the intake port center line, asshown in FIGS. 5A-B. Individual, equal length runners may pull off ofthe plenum to feed each cylinder of the engine 202 for consistent chargedistribution. The runners may be angled towards the incoming chargewhere they connect to the plenum in order to help direct flow down therunners to feed each cylinder. The individual runners offer additionalbenefits such as further separation of cylinders, so as to reduce oreliminate fuel cross-talk with a Port Fuel Injection (PFI) architecture.

The exhaust ports also include the BISE diamond valve pattern. Smallerexhaust valves and ports result in higher exhaust flow velocities thatpositively affect performance of the pulse EGR system 270. The pulse EGRsystem 270 performance may be improved by efficient exhaust flowpassages and junctions in order to minimize losses. The exhaust manifold210 provided a drastically lower loss factor to the turbine 260 and EGRsystem 270.

Turbomachinery

FIG. 6A is a perspective view of the exhaust manifold 210 of the systemof FIG. 3 fluidly coupled to a turbine 260 and FIG. 6B shows the exhaustmanifold 210 and turbine 260 assembled with covers positioned thereon.The turbine 260 is structured to provide every cylinder of the engine202 the same experience and minimize loss coefficient. The losscoefficient may be minimized by optimizing the trajectory and the areaschedule of the exhaust manifold 210.

Each cylinder of the engine 202 may be provided the same exhaust gasbackpressure by maintaining fully divided flows up to the turbine 260.In some embodiments, the turbine may comprise a twin port electronicallycontrolled waste gate to enable intake of exhaust gas flow from bothbanks of the exhaust manifold 210 (e.g., the plurality of outlet ports116), further providing an identical breathing experience for allcylinders.

Exhaust Gas Recirculation

FIG. 7 is a perspective view of an EGR system 270 included in the system200 of FIG. 3 . The engine 202 operates with a stoichiometric air/fuelration (AFR) and charge diluted with up to 25% EGR, while minimizingresiduals. In addition to the exhaust manifold features alreadydiscussed, a very efficient flow junction to combine the flows may beimplemented. The hot components of the EGR system 270 were developedconcurrently and coupled to the exhaust manifold 210. Concurrent withCFD analysis of the flow domain, thermal mechanical fatigue analysis ofthe designs was also performed to ensure durability.

Oil Control

A stable spark-ignited architecture may be achieved by eliminatingsources of knock and pre-ignition. One cause of knock and pre-ignitionmay include oil control and particularly from piston rings and valvestem seals. To address oil intrusion from the valve stem, a seal whichis four times drier than conventional seals is used. The seal is alsorated for vacuum, which may be beneficial on a throttled engine (e.g.,the engine 202) which frequently operates with a vacuum in the intakemanifold (e.g., the intake manifold 250). Oil intrusion past the pistonrings of the cylinders was prevented using a three piece oil ring whichhas improved ring dynamics (compared to a two piece oil ring), thereforeproviding improved oil control.

Cylinder Head and Spark Plug Cooling

A potential source of pre-ignition addressed in various embodiments isan overheated spark plug. FIG. 8A-B are finite element analysis (FEA)models showing heat transfer coefficients in water jackets around valveseats, bridges and an ignitor core of a cylinder included in the engineof FIG. 3 (FIG. 8A) and predicted combustion face temperature andlocation of max temperature (FIG. 8B).

As seen in FIGS. 8A-B, the heat transfer coefficients are highest in thebridges and surrounding the entire ignitor bore. The engine ignitor boreis structured such that all of the coolant flows past the ignitor bores,thereby providing exceptional cooling to the spark plug. Furthermore,the combustion face, particularly edges, are also effectively cooled soas to prevent hot spots and pre-ignition. As shown in FIG. 8B, thecombustion face is relatively cool. This not only prevents pre-ignition,it also ensures a durable and robust cylinder head with tolerance tobrief periods of knock and temperature rise.

Fuel System

The engine 202 hardware allows placement of port fuel injectors in twopossible locations and using two possible injectors. The injectors maybe placed in the intake manifold 250 runners and/or above the intakeports in the cylinder head of the engine 202. In some embodiments, theengine 202 operates with 100% single point fuel injection (SPFI) orupstream mixed, or 100% multi point fuel injection (MPFI) injected inthe individual ports. Additionally, in various embodiments, the engine202 may run with any mix of SPFI and MPFI. Combustion CFD predicted abenefit to using a port fuel distribution tube and engine 202 testingproved this to be the case.

An additional benefit of locating the fuel injectors above the port isintake manifold over pressure (IMOP), that is, intake backfiremitigation. With a single point injection near the intake throttle, theentire intake manifold 250 contains a stoichiometric combustiblemixture. With a MPFI system, most of the intake manifold 250 may befilled with air or possibly a very lean mixture beyond the ignitionlimits.

Compressor Bypass Valve

Stoichiometric gas engines are throttled by air (opposed to a dieselengine throttled by fueling) which may pose a challenge for the turbine260 (e.g., a turbocharger compressor). When the engine 202 quicklytransitions from a high boost condition to a no boost condition(tip-out), the throttle plate may slam shut and the high speed, highpressure charge between the compressor and the throttle may have to berelieved, otherwise the pressure may spike and find a low pressure pathback through the compressor. This is known as compressor surge and maycause a loading reversal of the compressor blades, which may quicklylead to fatigue failures.

In order to prevent this, an electronically controlled compressorrecirculation valve (CRV) was implemented. FIG. 9 is a schematicillustration of a compressor recirculation system 300, according to anembodiment. The compressor recirculation system 300 includes a CRV 302that is controllably actuated to prevent back flow of the intake air toa compressor 304. The CRV 302 is structured to be controllably opened toprovide a path to bleed off the high pressure air to prevent compressorsurge, particularly during tip-out events or at any suitable time tohelp prevent surge. The CRV 302 is controlled based on variousparameters, such as air pressure, compressor operating parameters,engine operating parameters, etc.

Engine Optimization

A stoichiometric with cooled EGR combustion system was coupled to theengine 202 as it has the capability to deliver high BMEP, extremely lowemissions and robust operation. The performance optimization anddevelopment of the engine 202 subsystems was split into three criticalareas: combustion system, fuel system, and charging system.

Combustion System

Development of the combustion system was focused on improvements inclosed cycle efficiency, reduced heat transfer and capability of shortburn durations under highly dilute conditions and short ignition delaytimes. High dilution was chosen in order to control componenttemperatures and to realize closed cycle efficiency improvements throughreduced heat transfer as shown in FIG. 10 .

Initial combustion system work was done using a full combustion cycleanalysis on a calibrated combustion CFD model. A baseline combustionsystem delivered 10% to 90% burn durations capable of tolerating highlevels of EGR dilution. The system 200 was structured to maintain thatburn duration with improved efficiency and ignition delay. FIG. 10 is aplot of impact of EGR on gross indicated efficiency of the engine. FIG.11A is a plot of burn duration and FIG. 11B is a plot of ignition delayvs. crank angle of 50% (CA50) variations.

The progression from iteration #1 to iteration #4 as shown in FIG. 10represents the investigation of swirl level along with charge motiondevelopment during the cycle and the impact to combustion. Iteration #1represents the best efficiency that was achieved because chargingpenalties were minimized representing the entitlement for efficiency.Iteration #2-#4 represent iterations to improve the burn duration withminimal impact to efficiency by influencing the in cylinder chargemotion. Trends in burn duration and ignition delay are shown in FIGS.11A-B. Iteration #4 was chosen as the combustion system for this engineas it was the best tradeoff for key deliverables. Fuel consumptiontrends are shown in FIG. 12 for constant EGR levels.

Fuel System

The benefit of a premix combustion system may comprise homogeneity ofthe fuel and air mixture. The disadvantages may comprise transportdelays, catalyst dither amplitude attenuation, and mitigation techniquesin the event of cylinder misfire. Challenges of port fuel injection aremixture stratification, number of physical parts and injection pressurerequirements. The benefits to MPFI may comprise cost, fuel controlcylinder by cylinder, transient response time and three-way catalyst(TWC) control. FIG. 13 are plots of premix air/fuel mixture injectionand port fuel injection (PFI) in each cylinder of the engine of FIG. 3 .Degraded combustion due to PFI was observed as shown in FIG. 13 .

Further work was done to understand if MPFI stratification could beimproved to match performance of the premixed combustion. FIG. 14 is aplot of apparent heat release vs. crank angle of a crank shaft of theengine of FIG. 3 operated using PFI. Many iterations of mixing devicesas well as injection strategies were assessed via combustion CFD inorder to compare combustion performance as shown in FIG. 14 . The MPFImixing observations yielded a design and injection strategy that wastransparent to the premix injection strategy allowing for advantages ofPFI to be realized.

Charging System

The charging system was structured to provide a uniform and equalmixture of air and EGR to each cylinder of the engine 202. In addition,the charging system was designed such that it could minimize the trappedresiduals. Additionally the turbine 260 was sized such that it couldaccommodate the lower flow rates of a stoichiometric engine 202 with EGR270 and provide the necessary pressure balance to drive the desired EGRlevels. The intake system was assessed for charge delivery and mixtureuniformity. With stringent requirements for charge uniformity and chargedistribution a final intake configuration as shown in the CFD model ofFIG. 15 was chosen.

The exhaust system was extensively tested and developed in order toensure good cylinder balance as well as facilitate an efficient exhaustevent. FIG. 16 shows a summary of iterations assessed using a novelmodeling approach in CFD to determine turbine loss factors. Theiterations were focused on geometric changes that improved losses in themanifold and balanced the losses cylinder by cylinder. Iteration #8 waschosen as the exhaust manifold 210 configuration for the engine 202.

Controls

Air Handling Control

FIG. 17 is a schematic diagram of an air handling (AH) system 310,according to an embodiment. The air handling system 310 includes theengine 202 FIG. 2 and the CRV 302 of FIG. 9 . The fresh air coming fromthe atmosphere enters the system 310 through an air filter 312. Pressureis raised by a compressor 314 of a turbocharger 316 and temperaturereduced by a charge air cooler (CAC) 318. This air reservoir togetherwith an Intake Air Throttle (IAT) 320 is used to control the air flowgoing into the intake manifold 250. Similarly, the EGR flow divertedfrom the exhaust manifold 210 is controlled by an EGR Valve (EGV) 322.Both air and EGR are mixed in the intake manifold 250 at ratescontrolled by the valves. Lastly, the compressor 314 is maintained awayfrom the surge region by actuating the CRV 302.

The exhaust gas not diverted to the intake manifold 250 is communicatedto a waste-gated turbine 324 of the turbocharger 316 where a waste gatevalve (WG) 326 is used to control what portion of the flow is bypassed.By doing so, the energy going to the turbine 324 and consequently theboost can be controlled within certain limits. The control comprisescalculating the IAT 320, EGV 322, and WG 326 actuator commands toachieve the target engine Fresh Air Flow (FAF), EGR fraction and/orboost.

In stoichiometric engines, FAF is directly related to engine power sothe target FAF is calculated from the driver torque request and enginespeed. EGR fraction, on the other hand, is used to reduce knock and PMEPand NO_(x). The EGR fraction target is usually calibrated as a functionof (at least) load and engine 202 speed. Finally, having three actuatorsallows the tracking of three references (when feasible). The last targetfor the air handling control is turbocharger boost, which allows totrade off transient performance with pumping efficiency. A common targetto exercise this tradeoff is the pressure drop on the IAT 320, which maybe stored, for example as a function of engine 202 load and speed.

The control was designed using physical models of the AH components,which significantly reduced the need for empirical table lookups toaddress system nonlinearities and changes in environmental conditions.The FAF and EGR fraction control performance is shown in FIG. 18 . FIG.18A is a plot of fresh air flow and FIG. 18B is a plot of EFR Fractiontracking during a federal testing procedure (FTP) cycle. Overall, theFAF and EGR Fraction remain on top of the reference with few exceptions,most of them related to turbo spooling. The large EGR fraction deviationduring idle regions corresponds to EGR flow measurement errors at lowflows. The actual tracking error is zero since the EGR valve 322 remainsclose during those regions.

Air Fuel Ratio Control

The conversion efficiency of the TWC is directly related to the AFR.Therefore, AFR is a strong lever to control the system out emissions.FIG. 19 is a schematic illustration of an air/fuel ratio control system,according to an embodiment. The AFR control system comprises a cascadecontrol system with two loops (inner loop and outer loop). The innerloop adjusts the on-time of the fuel injectors to precisely track theAFR target, while the outer loop determines the AFR target based on thecatalyst states for best conversion efficiency of the emissionconstituents.

The inner loop consists of feedforward and feedback fuel scheduling. Thefeedforward fueling schedules fuel injector on-time based on theestimated air mass in the cylinder, while the feedback trims thefeedforward calculation based on a wideband lambda sensor located afterthe turbocharger. Due to the slow response of the feedback loop, thetransient performance of the AFR control is mainly determined by thefeedforward fueling. The dynamics of the injectors can be neglected dueto its fast response time compared to the air dynamics. Therefore,accuracy of the air estimator plays the most important role in definingthe inner loop control performance. A physics-based approach, whichutilizes a charge virtual sensor and an EGR flow sensor, was developedto accurately predict air flow to the cylinder. FIG. 20A-B shows theon-engine validation of the air estimator at different engine speeds.

The outer loop consists of a feedforward mean AFR target table. Afeedback control trims the AFR target based on a wideband O₂ sensorlocated at midbed (between the first catalyst TWC1 and second catalystTWC2). The feedforward mean lambda values are pre-determined via steadystate catalyst characteristic testing at various engine 202 operatingconditions. The objective is to maintain a constant AFR target at themidbed location that optimizes the conversion of all the emissionsconstituents. FIGS. 21A-D are plots demonstrating the influence of outerloop control on constituents of an exhaust gas emitted from the system200 of FIG. 3 . FIGS. 21A-D shows the influence of the outer loopcontrol on the system out emissions. The benefit of having the outerloop control can be seen clearly from the individual plots. However, tomeet the ultra-low NO_(x) requirement, a trade-off among the emissionsconstituents may also be observed.

Aftertreatment

Various embodiments include a close-coupled after treatment architectureto meet system out ultralow NO_(x) emission requirement. The aftertreatment architecture consists of both a close-coupled TWC andunderfloor TWCs. This architecture provides a suitable compromisebetween high system efficiency and packaging constraints. The closecoupled aftertreatment architecture demonstrates excellent performancein managing both cold-start and warm-start transient emissions control.Furthermore, through benchmarking evaluation, “TWC technology A” wasselected to achieve both high NO_(x) conversion and methane (CH₄)conversion at near stoichiometric lambda (i.e., air/fuel ratio). Theplatinum-group metal (PGM) loading of the after treatment system wasengineered differently between the close-coupled and underfloor TWCs.

FIGS. 22A-C are plots of NO_(x), (FIG. 22A), CH₄ (FIG. 22B) and CO (FIG.22C) emissions during heavy-duty cold FTP transient cycle. The emissionswere reported at engine out (EO), close-coupled catalyst out (CC) andsystem out (SO) locations. During the cold FTP transient cycle as shownin FIGS. 22A-C, the close-coupled TWC effectively managed the first 0-50seconds NO_(x) emissions control before warming up the underfloorcatalyst. CH₄ emissions was largely controlled through close-coupled TWCfor the first 380 seconds. The close-coupled TWC successfully convertedover 70% of the cumulative engine out NO_(x) emissions and over 60% ofthe cumulative engine out CH₄ emissions during the cold FTP cycle.

FIGS. 23A-C are plots of NO_(x), (FIG. 23A), methane (FIG. 23B) and CO(FIG. 23C) emissions during heavy-duty warm FTP transient cycle. Theemissions were reported at EO. CC and SO locations. During the warm FTPtransient cycle as shown in FIGS. 23A-C, the close-coupled architectureconverted over 70% of the cumulative engine out NO_(x) emissions andover 65% of the cumulative engine out CH₄ emissions during the warm FTPcycle.

Various embodiments include a TWC model that is capable of closelypredicting the application cycles emissions for natural gas application.Key challenges of developing such a model include dynamic oxygen storagemechanism, complex CH₄ oxidation and reforming kinetics and itsinteraction with the oxygen storage dynamics, and the highly transientnature of the air-fuel ratio control during the TWC application. Theaccuracy of such a TWC model may also depend on obtaining the rightkinetic mechanisms through well-designed tests and reliable datacollection.

A global-kinetic TWC model was developed and validated using aproduction natural gas engine with an underfloor only after treatmentsystem during transient emissions cycles (e.g. cold Federal TestProcedure cycle, warm Federal Test Procedure cycles and World HarmonizedTransient Cycles). FIG. 24A is a plot of cumulative NO_(x) and FIG. 24Bis a plot of cumulative CH₄ cold FTP transient cycle conversionperformance predictions against testing data. As shown in FIGS. 24A-B,the model has a high predictability of aftertreatment CH₄ and NO_(x)performance during the cold FTP cycle against engine bench testingresults.

System Integration

A system approach was used to develop a system that was capable of 90%reduction in NO_(x) below current standards and has equivalentefficiency to a diesel engine. With the intake manifold 250, EGRassembly 270, exhaust manifold 210 and combustion systems as describedherein, the robustness of the engine 202 was dramatically improved.Robustness of the engine 202 is depicted in FIG. 25 which includes plotsof a peak cylinder pressure (PCP) and CA50 variations of a baseline andthe engine 202 (also referred to as “the new engine”) and showimprovements in cylinder to cylinder and cycle to cycle variation atpeak torque with three sigma error bars for reference. The reduction invariation across the engine 202 allows for better control of the engine202, enables lower emissions capability, improved robustness/operatingrange, higher engine efficiency and capability for increased powerdensity.

In addition to variation reduction, component durability was alsoaddressed. An important component involved in engine durability is thecylinder head. A comparison of the head temperatures is shown in FIGS.26A-B which are FEA models comparing a combustion face temperature ofthe baseline engine (FIG. 26A) and the new engine (FIG. 26B). The headtemperatures were improved through a revised design so as to reduce themaximum temperatures as well as provide uniform cooling of thecombustion face. A comparison of the baseline and the new engine areshown below.

In addition to the cylinder head the exhaust system utilized improvedhigh temperature materials for durability as well as revised designs toimprove the loss coefficient of the manifold and improve therelationship between EGR fraction and engine delta p as shown in FIG. 27.

The ability to drive large amounts of EGR with low engine delta p mayallow for reduced residuals supporting a wide operating range for EGR athigh load conditions which provides further robustness to knock. Anexample of the EGR Range at high load is shown in FIG. 28 for the peaktorque condition.

With a significantly improved engine design, controls were redesigned aswell to enable improved air handling, combustion and air/fuel ratiocontrols. The control system is capable of delivering the transientresponse, robustness and efficiency while at the same time deliveringtight control for NO_(x) emissions reduction. The tracking performanceof the air handling system is shown in FIG. 29 .

Using the system described herein 90% reduction NO_(x) emissions belowcurrent standards was achieved. The emission results are shown in FIG.30 . A cold/hot FTP emissions test was utilized to demonstratecompliance with the objectives of 0.02 g/hp-hr, according to variousembodiments. In addition to the reduced NO_(x) emissions the fueleconomy was significantly improved over the baseline engine satisfyinganother target to demonstrate equivalent fuel consumption to a dieselengine. Results are shown in FIG. 31 .

It should be noted that the term “example” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

The terms “coupled,” and the like as used herein mean the joining of twomembers directly or indirectly to one another. Such joining may bestationary (e.g., permanent) or moveable (e.g., removable orreleasable). Such joining may be achieved with the two members or thetwo members and any additional intermediate members being integrallyformed as a single unitary body with one another or with the two membersor the two members and any additional intermediate members beingattached to one another.

It is important to note that the construction and arrangement of thevarious exemplary embodiments are illustrative only. Although only a fewembodiments have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter described herein.Additionally, it should be understood that features from one embodimentdisclosed herein may be combined with features of other embodimentsdisclosed herein as one of ordinary skill in the art would understand.Other substitutions, modifications, changes and omissions may also bemade in the design, operating conditions and arrangement of the variousexemplary embodiments without departing from the scope of the presentinvention.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features described in this specification in thecontext of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresdescribed in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

What is claimed is:
 1. An intake manifold, comprising: a first inletstructured to receive pressurized intake air from a turbocharger; asecond inlet structured to receive exhaust gas recirculation gas from anexhaust gas recirculation system; a third inlet structured to receivefuel from a fuel line; a plurality of outlets structured to be fluidlycoupled to an engine; and an intake manifold passage extending betweeneach of the first, second, and third inlets, and the plurality ofoutlets, the intake manifold passage shaped so as to cause at least tworeversals in flow direction of each of the intake air, the exhaust gasrecirculation gas, and the fuel through the intake manifold passage soas to improve mixing of each of the intake air, the exhaust gasrecirculation gas, and the fuel.
 2. The intake manifold of claim 1,wherein the intake manifold passage is “S” shaped.
 3. The intakemanifold of claim 2, wherein each of the plurality of drop-down runnershave an equal length.
 4. The intake manifold of claim 1, wherein theintake manifold passage defines a plenum, and further comprising aplurality of drop-down runners from the plenum to the plurality ofoutlets.
 5. The intake manifold of claim 4, wherein the plurality ofdrop-down runners are configured to receive placement of port fuelinjectors therein.
 6. The intake manifold of claim 4, wherein the plenumis positioned above a center line of the plurality of outlets.